Support prop

ABSTRACT

A support prop which includes telescopically interengaged inner and outer tubular members, a one-way valve for introducing pressurized liquid into a volume inside at least one of the members, a pressure relief valve for releasing liquid from the volume when the liquid pressure in the volume exceeds a predetermined value and a number of wedges which are located between opposing surfaces of the tubular members and which are engaged with one member and which deform the inner member when telescopic yielding action of the members takes place.

BACKGROUND OF THE INVENTION

This invention relates to a support prop suitable for use in an underground excavation, for providing support between a hanging wall and an opposed foot wall.

An object of the invention is to provide a support prop which can be pre-stressed, at the time of installation, so that the prop can provide its rated load-bearing capability as soon as possible and which, thereafter, can yield at a controlled rate which can be varied, within reason, according to requirement by user selection process.

SUMMARY OF THE INVENTION

The invention provides a support prop which includes:

-   (a) an outer elongate tubular member with an inner surface, an     interior bounded by the inner surface, a first end which has an open     mouth, a second end and a plate which is engaged with, and which     seals, the second end, -   (b) an inner elongate tubular member with an outer surface, a     leading end, a trailing end, and a closure which is engaged with,     and which seals, the leading end, -   (c) the inner tubular member and the outer tubular member being     aligned in an axial direction with said leading end being inserted     into said open mouth so that the inner tubular member extends     telescopically into the outer tubular member, -   (d) a seal which is engaged with the closure and which is in sliding     contact with said inner surface whereby a volume in at least the     outer tubular member is enclosed by a portion of said inner surface,     the plate and the closure at said leading end, -   (e) an inlet valve, secured to the outer tubular member, through     which liquid can be introduced into said volume thereby to     pressurise the volume, -   (f) a pressure relief valve engaged with the closure, the pressure     relief valve allowing liquid, in the volume, at a pressure in excess     of a predetermined level, to flow from the volume through the     pressure relief valve into said interior, -   (g) at least one wedge member located between opposing sections of     said outer surface and said inner surface, and -   (h) wherein the inner tubular member is movable in said axial     direction into the outer tubular member against a yielding force     which is determined by -   (i) said predetermined pressure level, and -   (ii) deformation of the inner tubular member by the at least one     wedge member which is movable, together with the inner tubular     member, into the outer tubular member.

The seal is preferably a cup seal positioned at a periphery of the closure, facing said volume. In this way a positive pressure effect is achieved i.e. as the pressure in the volume increases the effectiveness of the seal is automatically increased.

The wedge member may be one of a plurality of similar wedge members. The invention is not limited in this regard. Preferably the wedge member includes a body which, in said axial direction, is tapered in cross-section and which, in cross-section in a direction which is transverse to said axial direction, has a curved shape. Preferably a surface of the wedge member which opposes said outer surface is serrated.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is further described by way of example with reference to the accompanying drawings in which:

FIG. 1 illustrates in cross-section a support prop according to the invention, and

FIGS. 2 and 3 are different views of a wedge member used in the support prop.

DESCRIPTION OF PREFERRED EMBODIMENT

FIG. 1 of the accompanying drawing illustrates from one side and in cross-section a support prop 10 according to the invention.

The prop includes an outer elongate tubular member 12 with an inner surface 14, a first end 16 which has an open mouth 18, a second end 20, and a plate 22 which is welded to the second end so as to seal the second end.

The prop further includes an inner elongate tubular member 38 with an outer surface 30, a leading end 32, a closure 34 which is engaged with and which seals the leading end, and a trailing end 36 which is covered by a plate 38.

A cup seal 40 is fixed to a peripheral edge 42 of the closure. The cup seal automatically is in sealing contact with the closure. The cup seal bears on the inner surface 14 and is in sliding contact therewith.

A pressure relief valve 50 is fixed to the closure and overlies an aperture 52 in the closure. The pressure relief valve is of a type known in the art and allows liquid to flow through inlet apertures 54 in a side of the valve to an outlet 56 which is aligned with the aperture 52 when the pressure difference between the inlet and outlet apertures exceeds a predetermined level. The level can be set according to requirement using techniques which are known in the art.

A one-way inlet valve 60 is fixed to the outer tubular member 12. The valve 60 is in communication with a volume 62 which is bounded by the closure, part of the inner surface 14 and the plate 22.

The mouth 18 of the member 12 is slightly flared. A number of wedge members 70 are located in a small annular interface between opposing sections of the outer surface 30 and of the inner surface 14.

FIG. 2 shows, on an enlarged scale, a wedge member 70 from one end while FIG. 3 shows the wedge member in cross-section, taken on a line 3-3 in FIG. 2.

The wedge member has a body 74 which is curved. The curvature corresponds to the curvature of the interface between the outer surface 30 and the inner surface 14 of the tubular members.

The body 74 has an inner side 76 and an outer side 78. Referring to FIG. 3 it can be seen that the body has a tapered dimension and decreases in cross-sectional dimension from an upper end 80 towards a lower end 82. The inner surface 76 is stepped, and is formed with a number of serrations 84. The outer surface 78 is smooth. A small channel 90 is formed, in a circumferential sense, in the outer surface.

The wedge member has a first wedge angle 84A which is of the order of 15° and which facilitates placement of the wedge member between opposing surfaces of the inner and outer tubular members. This is followed by an increased wedge angle 84B which typically is of the order of 25°.

A tie, not shown, is positioned in the channel 90 to keep the wedge member attached to the remainder of the support, e.g. for transport and storage purposes.

In use of the prop the plate 22 is positioned on a foot wall 94 in an underground excavation 96 and plate 38 at the trailing end is opposing a hanging wall 98 in the excavation. Pressurized liquid, e.g. water, is introduced through the one-way filler valve 60 into the volume 62. At this stage the wedge members 70 are not present. The volume 62 is expanded in an axial direction 100 and the tubular members are thereby telescopically extended. The pressure inside the volume 62 is well below the release pressure of the valve 50.

The volume 62 is pressurized in order to bring opposing surfaces of the prop into contact with the foot wall and the hanging wall respectively. Further pressurization places the prop under an axially directed compressive loading force, to a predetermined level, to pre-stress the prop. This is a desirable feature for it enables the prop to take up its desired load-bearing capability at the time of installation.

After the prop has been hydraulically installed, in the manner described, a number of the wedge members 70 are placed into the gap between the flared mouth 18 and the outer surface 30. The wedge members are tapped into the interface using a hammer or similar tool. In this way the serrations 84 are brought into frictional and mechanical engagement with the outer surface 30.

As noted the leading wedge angle 84A is relatively small, about 15°, and this helps in the initial placement of each wedge member into the gap.

If closure of the hanging and foot wall takes place then the pressure in the volume 62 is increased. When the release pressure of the valve 50 is exceeded water can flow through the apertures 52 and exit from the valve into the interior of the tubular member 30. This provides a pressure release function and the prop is therefore capable of yielding at a controlled rate which is determined by the setting of the valve. The wedge members are formed between the outer surface 30 and the inner surface 14. The inner tubular member can only move into the outer tubular member if the wedge members deform the inner tubular member.

The deformation of the inner tubular member is primarily attributable to the increase in the wedge angle to 84B. It is this wedge angle which can be varied to control the yielding action of the prop, in one respect.

The inner tubular member is preferably made of a thinner gauge material than the outer tubular member. This promotes deformation of the inner tubular member, rather than the outer tubular member. This occurs despite the serrations 84 which assist to drag each wedge to the end of the flared portion of the outer tubular member.

The net effect is that the yielding action of the prop is controlled by two factors, namely the setting of the pressure relief valve and the deformation action of the wedge members.

The pressure relief valve can be chosen according to requirement and its setting can be determined beforehand taking into account a particular application, yield rate and the like. Similar considerations apply in respect of the wedge members. Firstly, the number of wedge members can be varied. Secondly, the size of each wedge member and, in particular, its length and wedge angle can also be varied according to requirement to achieve an appropriate yielding effect. The wedge angle 84B is, as noted, typically of the order of 25°. It can be varied from as low as 15° to promote rapid yielding to a value as high as 40° to create a situation in which a high force is required before yielding takes place. A particular benefit in this respect is that, at the time of installation, a particular yielding action can be provided for purely by selecting and using the wedge members appropriately. 

1. A support prop which includes: (a) an outer elongate tubular member with an inner surface, an interior bounded by the inner surface, a first end which has an open mouth, a second end, and a plate which is engaged with, and which seals, the second end, (b) an inner elongate tubular member with an outer surface, a leading end, a trailing end, and a closure which is engaged with, and which seals, the leading end, (c) the inner tubular member and the outer tubular member being aligned in an axial direction with said leading end being inserted into said open mouth so that the inner tubular member extends telescopically into the outer tubular member, (d) a seal which is engaged with the closure and which is in sliding contact with said inner surface whereby a volume in at least the outer tubular member is enclosed by a portion of said inner surface, the plate and the closure at said leading end, (e) an inlet valve, secured to the outer tubular member, through which liquid can be introduced into said volume thereby to pressurise the volume, (f) a pressure relief valve engaged with the closure, the pressure relief valve allowing liquid, in the volume, at a pressure in excess of a predetermined level, to flow from the volume through the pressure relief valve into said interior, (g) at least one wedge member located between opposing sections of said outer surface and said inner surface, and (h) wherein the inner tubular member is movable in said axial direction into the outer tubular member against a yielding force which is determined by (i) said predetermined pressure level, and (ii) deformation of the inner tubular member by the at least one wedge member which is movable, together with the inner tubular member, into the outer tubular member.
 2. A support prop according to claim 1 wherein the seal comprises a cup seal, on a periphery of the closure, which faces said volume.
 3. A support prop according to claim 1 wherein the wedge member includes a body which, in said axial direction, is tapered in cross-section, and which, in cross-section in a direction which is transverse to said axial direction, has a curved shape.
 4. A support prop according to claim 3 wherein a surface of the wedge member, which opposes said outer surface, is serrated.
 5. A support prop according to claim 3 wherein said tapered cross-section has a wedge angle of from 15° to 40°. 